Planning and Optimization Methods for Advanced Urban Logistics Systems at Tactical Level - Sustainable Urban Logistics: Concepts, Methods and Information Systems - page 142

distribution to reach a higher level of efficiency (Mancini 2013a ). This goal may be
achieved through a better exploitation of presently available resources, a clever
planning of the whole distribution process, a smart network design and a strictly
collaboration among shipping companies. Such kind of approach implies the
consolidation of loads of different shippers and carriers on the same vehicle, or,
more generally, on the same service, and an efficient coordination of the resulting
transportation activities. One of the most efficient ways to implement goods
consolidation is to adopt multi-stage LTL transport systems (Gonzalez-Feliu
2012a ), which allow to split the transportation chains in different legs, in each one
of which, goods are consolidated at facilities, where they are sorted and carried on
other vehicles which perform the delivery to the customers or to another set of
facilities.
The specificities of the last mile of the supply chains (mainly LTL transpor-
tation, with less optimized vehicles and confronted in many cases to big con-
straints and unexpected events related to the congestion of urban and peri-urban
infrastructures) and the increase of customer satisfaction approaches in supply
chain management make important to relate the quality to the logistics costs,
making the economic aspects of the last mile an important component of supply
chain design. In this context, the new advances in technologies have been a
positive factor for the development of new markets and new consumer needs: the
growth of e-commerce and postal shopping, as well as the pace of life, have
reinforced the importance of ''just in time'' policies in freight distribution.
Moreover, the service quality of a transportation carrier is often related to travel
time, and can vary according to both socio-economics and trip characteristics. The
total travel time of a vehicle trip depends on several aspects, like actual travel
time, waiting and access time, congestion, deadlines or service features, etc. In
addition, the new constraints of the generalised economic and financial crisis make
a readjustment on the freight transportation strategies that have to be included in
the main logistics tactical decisions. For these reasons, it is important for a dis-
tribution system to ensure the efficiency while maintaining a service quality
defined by the time windows or other quality indices. For this reason, after defining
the system, it is important to ensure that in a middle term period, the system is
well-managed and controlled. To do this, several methods from the operations
research and combinatorial optimization can be defined.
The aim of this chapter is to propose a guide for researchers and practitioners on
the main methods related to tactical planning in urban logistics. Two main families
of problems will be addressed: vehicle routing with time windows and multi-stage
vehicle routing. The chapter is organised as follows. Next section provides a brief
background of freight transportation problems in urban logistics and motivates the
aim and scope of the chapter. After that, a focus on two-stage VRP will be made,
presenting the main issues, problems and variants. Finally, a qualitative analysis
on the development of such systems will be carried out.